Question

A coin is kept on a graph phone disc with its centre at a distance of 5 cm from the centre of the disc and the disc is set into rotational the coin beings to sleep when the disc just reaches a speed of 45 rotational per minute find the coefficient of fractions between the coin and the disc

Answer 1

Given that, r=5 cm=0.05 m,

n=90 r.p.m.=1.5 Hz

Limiting force of static frictions =Centrifugal force

μ

s

mg=mrω

2

∴μ

s

=

g

rω

2

=

g

r(2πn)

2

∴μ

s

=

g

4π

2

n

2

r

=

9.8

4×0.05×(3.14)

2

×(1.5)

2

∴μ

s

=0.4527